Stroke, Parkinson's disease, Alzheimer's disease, Pick's disease, Huntington's disease, amyotrophic lateral sclerosis, traumatic central nervous system disease and spinal cord injury disease involve dysneuria caused by injury of nerve cells, and they have been generally treated by medication or surgical operation which may severely damage normal cells.
Recently a cell replacement therapy in which normal cells are transplanted to replace destroyed or damaged cells has been recognized to be effective for such diseases, and stem cells, in particular, which can be differentiated and proliferated into desired tissues are under intense studies.
Stem cells are unspecialized cells that can be proliferated unlimitedly in the undifferentiated stage and can be differentiated into diverse tissues in response to specific stimuli.
Neural stem cells, from which neurons and/or glia such as astrocytes, oligodendrocytes and/or Schwann cells form, are also undifferentiated cells having self-reproduction potency. They differentiate into neural cells, for example neurons or glia via neural precursor cells or glia precursor cells.
Mesenchymal stem cells, which differentiate into bone, cartilage, adipose tissue, muscle, tendon, ligament, neural tissue and others, have been known to be viable for the cell replacement therapy. Mesenchymal stem cells have been obtained mainly from bone marrow, but such mesenchymal stem cells provide only limited applications due to their restrictive potency for differentiation and proliferation. Further, complicated and often painful operations composed of several steps must be conducted for such cell replacement therapy, besides the problem of finding a donor who has histocompatibility antigens identical with that of a patient to exclude graft versus host reaction during bone marrow transplantation.
In recent years, the umbilical cord blood has become a target for researchers because of its high concentrations of stem cells. A number of trials to treat blood diseases by transplanting umbilical cord blood to a patient have been conducted, and umbilical cord blood banks, which preserve umbilical cord blood in a frozen form until use, have been established for the autologous transplantation therapy.
Unlike the bone marrow, the umbilical cord blood can be obtained by a simple operation from an umbilical cord and it causes little graft versus host reaction. For these reasons, worldwide studies for clinical application of the umbilical cord blood have recently been performed.
The present inventors have also extensively studied umbilical cord blood-derived mesenchymal stem cells and found that they are capable of inducing differentiation and proliferation of neural precursor cells or neural stem cells to neural cells.